In a 3-phase, 4-wire system, the triplen harmonic currents (3, 9, 15, 21…) sum in the neutral wire because they are all in-phase. This is why the neutral current can be much higher than the phase currents even on an otherwise balanced load application.
Why neutral current is more than phase current?
The Neutral current could be higher then Phase current because of harmonics in the electrical system caused by switch mode power supplies in a large office building with a lot of computers. Triple N harmonics could cause Neutrals to burn out under extreme conditions.
What causes a high neutral current?
High neutral currents can be caused by unbalanced and/or non-linear loads with high harmonics. K-rated transformers have a 200% rated neutral. Amperage should be measured with a meter capable of measuring true RMS currents.
Why neutral current is increased when the 3-phase load is unbalanced?
In an unbalanced 3 phase electrical load, the line currents are different, which causes the neutral current to flow from the star point of the load to the supply star point. If the neutral wire is broken or disconnected, the out of balanced current cannot return to the supply through the star point, but it must return.
What is the effect of high neutral current?
High neutral currents in power systems can cause overloaded power feeders, overloaded transformers, voltage distortion, and common mode noise[8-10]. Three-phase, four-wire building power feeders are often sized based on three current-carrying conductors in a conduit.
What should be neutral current?
In an ideal balanced sinusoidal three-phase power system, the neutral current is the vector sum of the three phase currents, should be equal to zero. Under normal operating condition, some phase unbalance occurs resulting in a small neutral current.
Does the neutral wire carry a current?
The neutral wire will be connected to the earth ground, the color of the neutral wire could be grey or white. During normal operations, the neutral wire will carry current. We can see neutral in most of the electrical equipment, mostly in non-linear loads.
Does neutral carry current in single phase?
Yes, neutral wire carries current in a single phase. The single-phase power distribution consists of the phase and neutral wire for proper electricity distribution. While the phase wire carries the load, the neutral wire provides the path to return the current from the phase wire.
How can neutral current be reduced?
The closed loop control of the active power filter guarantees cancellation of neutral current harmonics under varying load conditions. The neutral current In is sensed via a current sensor and is processed through a 50 Hz notch filter in order to remove any fundamental current component in In.
